# NTSB WPR18LA252: Guimbal Cabri, N401SH, Santa Ana, CA, September 3, 2018 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: September 3, 2018, 15:37 local (22:37 UTC) - Place: Santa Ana, CA - Coordinates: 33.671943, -117.8675 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.6719&lon=-117.8675&mi=10 - Phase of flight: [Emergency descent](https://openairdocs.org/ntsb-phases/600) (OpenAirDocs' grouping) - Defining event: [Autorotation: Miscellaneous/other](https://openairdocs.org/ntsb-events/900) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration, Bureau d’Enquêtes et d’Analyses - NTSB case key (mKey): 98236 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR18LA252 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/98236/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=98236 - Page: https://openairdocs.org/ntsb/WPR18LA252 ## Probable cause The flight instructor's delayed application of power during a power recovery following an autorotation, which resulted in an unrecoverable low rotor rpm during the landing flare and subsequent loss of control. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine controls](https://openairdocs.org/ntsb-findings/01057600): Aircraft › Aircraft power plant · Incorrect use/operation (probable cause); cases with it: [Helicopteres Guimbal CABRI G2, 1 case](https://openairdocs.org/ntsb-findings/01057600/cases.md?model=9000001), [All aircraft, 51 cases](https://openairdocs.org/ntsb-findings/01057600/cases.md) - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Instructor/check pilot (probable cause); cases with it: [Helicopteres Guimbal CABRI G2, 11 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=9000001), [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Autorotation: Attempted remediation/recovery](https://openairdocs.org/ntsb-events/060); cases with it: [Helicopteres Guimbal CABRI G2, 6 cases](https://openairdocs.org/ntsb-events/060/sequence.md?model=9000001), [All aircraft, 1,422 cases](https://openairdocs.org/ntsb-events/060/sequence.md) - [Autorotation: Miscellaneous/other](https://openairdocs.org/ntsb-events/900) (defining event); cases with it: [Helicopteres Guimbal CABRI G2, 1 case](https://openairdocs.org/ntsb-events/900/sequence.md?model=9000001), [All aircraft, 1,556 cases](https://openairdocs.org/ntsb-events/900/sequence.md) - [Autorotation: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Helicopteres Guimbal CABRI G2, 10 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=9000001), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The flight instructor and private pilot receiving instruction (pilot) initiated a practice autorotation from about 700 ft in the airport traffic pattern. As the helicopter reached about 150 ft, the instructor slightly opened the twist grip throttle to initiate a power recovery but realized shortly thereafter that the applied power was insufficient to arrest the helicopter’s autorotative descent. The instructor applied additional power, and as the helicopter reached 40 ft, the pilot receiving instruction raised the collective, but the helicopter continued to descend in a flat attitude. The instructor then advanced the twist grip to full power but reported that the engine power did not increase as expected. The low rotor rpm horn activated, the nose yawed left, the helicopter rolled to the left, and the main rotor blades impacted the ground, resulting in substantial damage. A detailed examination of the collective control, twist-grip throttle, and governor control system revealed no pre-impact mechanical anomalies. It is likely that the flight instructor could not apply sufficient power to abort the practice autorotation following the pilot’s collective input, which resulted in an unrecoverable low rotor rpm condition and subsequent loss of control. The helicopter’s flight manual stated that the lowest recommended height for aborting an autorotation was 300 ft; however, the instructor initiated the recovery at 150 ft, which resulted in reduced time and altitude available to recognize that the engine was not responding as expected and continue with a power-off, touchdown autorotation. In a service letter published after the accident, the manufacturer advised against initiating a power recovery from an autorotation in the flare, as it could result in a loss of yaw control upon application of maximum engine torque. ## Factual narrative On September 3, 2018, about 1537 Pacific daylight time, a Guimbal Cabri G2 helicopter, N401SH, was substantially damaged when it was involved in an accident near Santa Ana, California. The flight instructor and private pilot receiving instruction were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. According to the instructor and pilot receiving instruction, they returned to the departure airport after conducting cross-country flight training and initiated an autorotation to simulate an inflight loss of engine power from about 700 ft mean sea level (msl). They maintained 50 kts throughout the autorotative descent, and upon reaching 150 ft msl, the instructor prepared for a power recovery by slightly opening the throttle. Two seconds later, the instructor realized that the helicopter did not have adequate power to arrest the descent and advanced the throttle further. The instructor added that as the helicopter reached 40 ft msl, the pilot raised the collective pitch control to stop the descent but did not complete the flare. While descending in a nearly flat attitude, the instructor rolled the throttle to its full-power position to complete the power recovery, but the engine power did not increase as anticipated. The low rotor rpm horn engaged, and the nose yawed to the left. The helicopter rolled to the left from about 4 ft above the ground before coming to rest on its left side. Postaccident photos furnished by the helicopter operator showed substantial damage to the main rotor blades and that the fuselage had separated from the skid attachment points. The instructor held a flight instructor certificate with ratings for helicopter and instrument helicopter. She reported 819 total hours of flight experience, all of which were in rotorcraft. She reported 15 total hours of flight experience in the accident helicopter at the time of the accident. The pilot receiving instruction held a private pilot certificate with a helicopter rating. He reported 99 total hours of flight experience, all of which were in rotorcraft. He reported 13 total flight hours in the accident helicopter at the time of the accident. The helicopter flight manual, under section 7-5.1, Autorotation training, stated: …the instructor should keep in mind that aborting autorotation should not be decided in the flare, when there is too much workload and that low rotor speed could prevent adequate yaw control… If power recovery is decided during autorotation: Roll-in throttle until governor engages, Gradually raise collective pitch to stop autorotation and descent, Control yaw during power recovery with pedals Note: …Be prepared to yawing to the left when power recovers. The flight manual also advised that the lowest recommended altitude for aborting an autorotation was 300 ft. Guimbal Helicopters Service Letter SL 19-002, Controllability in Yaw at Low Rotor Speed, published several months after the accident, warnedagainst ending an autorotation with a power recovery during or just after the flare. When performing a power recovery, the engine governor will re-engage as soon as the engine speed reaches 2,000 rpm and will fully open the throttle. With the engine torque at maximum, this could lead to a loss of yaw control. Airframe Examination Examination of the helicopter revealed that the lower left side fuselage and aft left skid crossbar exhibited some scraping. Each of the three main rotor blades tips were destroyed and the blades exhibited some bending opposite the direction of rotation. The main rotor mast and hub did not show any abnormalities, as the pitch change links were connected to each of their respective main rotor hub brackets. The elastomeric bearings were normal in appearance and did not exhibit any extrusion. The anti-torque pedals moved normally and were continuous to the tail rotor blades at the fenestron. The collective twist grip was advanced to the full power position multiple times from the mechanical idle position. The twist grip and governor performed as designed with no anomalies noted. The governor was also functionally tested in accordance with the maintenance manual. Testing showed that the governor functioned normally and could be overridden successfully by the twist grip as designed. Helicopter Flying Handbook The FAA Helicopter Flying Handbook (FAA-H-8083-21B), when describing a practice autorotation with power recovery procedure, stated: If the throttle is increased too fast or too much, an engine overspeed can occur; if throttle is increased to slowly or too little in proportion to the increase in collective pitch, a loss of rotor rpm results. ## Aircraft - Registration: [N401SH](https://openairdocs.org/aircraft/N401SH), registered now, S/N 1195, built 2017 (OpenAirDocs) - Reported make and model: Guimbal CABRI (G2) - Registry model: [Helicopteres Guimbal CABRI G2](https://openairdocs.org/model/helicopteres-guimbal-cabri-g2) (registry code 9000001) (OpenAirDocs) - Registry engine: [Lycoming O-360-J2A](https://openairdocs.org/engine/lycoming-o-360-j2a) (registry code 42314, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 1195 - Year built: 2017 - Airframe hours: 436.5 - Engines: Lycoming Engines O-360-J2A 160 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Operator: One Above Aviation - Registered owner: Spitzer Helicopter LLC - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, August 9, 2018, 47 hours before - Departed: SNA, Santa Ana, CA - Destination: SNA, Santa Ana, CA - Airport: SNA, John Wayne Airport-Orange Coun, runway 20L, 2,887 × 75 ft, asphalt - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 29; injuries: none; flight instructor; instrument ratings: helicopter; medical: class 2, with waivers/limitations; last flight review October 6, 2017; seat: left; restraint: 4-point; flight hours: 819 total, 15 in this make and model, 758 as pilot in command, 198 in the last 90 days, 81 in the last 30 days, 3 in the last 24 hours - Student pilot; age 23; injuries: none; private; medical: class 3, without waivers/limitations; last flight review July 25, 2018; seat: right; restraint: 4-point; flight hours: 99 total, 13 in this make and model, 18 as pilot in command, 34 in the last 90 days, 11 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 230° at 9 knots - Visibility: 10 statute miles - Temperature: 77 °F, dew point 63 °F - Altimeter: 29.82 inHg ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20180903012969A](https://openairdocs.org/incident/20180903012969A), Sep 3, 2018: Helicopteres Guimbal CABRI G2, Santa Ana, CA, Substantial damage. NTSB: on September 3, 2018, about 1537 pacific daylight time, a guimbal cabri G2 helicopter, N401SH, was substantially damaged during an autorotative landing… ## Docket (9 files) The files NTSB released with the investigation on June 3, 2021, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=98236. 14.5 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 3.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9070684&FileExtension=pdf&FileName=6120_Redacted-Rel.pdf - Weather reports and records (item 2, PDF, 2 pages, 61 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9194597&FileExtension=pdf&FileName=MOR%20Weather-Rel.pdf - Record of conversations (item 3, PDF, 5 pages, 68 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9195270&FileExtension=pdf&FileName=Record%20of%20conversations-Rel.pdf - NTSB examination report (item 4, PDF, 9 pages, 1.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9306988&FileExtension=pdf&FileName=NTSB%20Examination%20Report-Rel.pdf - Excerpt from aircraft logbooks (item 5, PDF, 3 pages, 973 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9194784&FileExtension=pdf&FileName=Excerpt%20from%20aircraft%20logs_Redacted-Rel.pdf - Service letter sl 19-001 (item 6, PDF, 6 pages, 5.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9193898&FileExtension=pdf&FileName=SL%2019-001%20A_%20Throttle%20Management%20During%20Simulated%20Engine%20Failure-Rel.pdf - Service letter sl 19-002 (item 7, PDF, 8 pages, 314 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9193573&FileExtension=pdf&FileName=SL%2019-002%20A_%20Controllability%20in%20Yaw%20at%20Low%20Rotor%20Speed-Rel.pdf - Excerpt from rotorcraft flight manual (item 8, PDF, 4 pages, 153 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9193582&FileExtension=pdf&FileName=Excerpt%20from%20Flight%20Manual-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 9, PDF, 2 pages, 2.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9319764&FileExtension=pdf&FileName=N401SH%20Spitzer_Redacted-Rel.pdf From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.